1. The Field of the Invention
The present invention is related generally to processes for converting biomass to gasoline products. More specifically, the present invention is related to a catalytic process for production of reformulated, partially oxygenated gasoline from lignin.
2. The Relevant Technology
The growing pollution problems in the United States and around the world are associated to a significant extent with undesirable side reactions during combustion of currently used fuels including gasolines and jet fuels. Conventional gasoline products were characterized in the past by a major proportion of aromatic hydrocarbon components, which, upon combustion, yield unacceptably large amounts of carbon monoxide and health-endangering levels of polycyclic carcinogens. The need for reformulation of gasoline, i.e., a significant change in the chemical composition of gasoline, has been recognized through a 1990 amendment of the Clean Air Act, which requires a lowering in the total aromatic content of gasoline to a maximum of 25 weight percent (wt-%), and a lowering in the concentration of a particular, strongly carcinogenic component, benzene, down to a level of less than 1 wt-%. Furthermore, the same amendment requires that the oxygen content of reformulated gasoline should be 2 wt-% or greater.
Reformulated gasoline compositions having somewhat lower concentrations of aromatic components and appropriate concentrations of oxygen-containing components, which are cleaner burning and markedly more environment-friendly than conventional current gasolines, are thus needed in order to comply with the Clean Air Act.
Prior processes concerned with petroleum-based reformulated gasoline compositions use several well-defined types of chemical reactions, including (a) alkylation of C.sub.3 to C.sub.5 olefins with branched C.sub.4 and C.sub.5 paraffins to produce higher branched paraffins in the gasoline boiling range; (b) skeletal isomerization of normal C.sub.4 and C.sub.5 olefins to produce branched C.sub.4 and C.sub.5 olefins, i.e., olefins containing tertiary carbons, which are needed for subsequent use in the production of appropriate ethers as additives for reformulated gasolines; (c) ring hydrogenation of aromatic hydrocarbons to reduce the aromatic content of naphthas and gasoline blends; (d) skeletal isomerization of normal paraffins to produce branched paraffins in the gasoline boiling range; and (e) etherification reactions of branched olefins to produce alkyl t-alkyl ethers, e.g., methyl t-butyl ether, ethyl t-butyl ether; methyl t-pentyl ether, and others, which are useful as oxygenated components of reformulated gasolines. In some of the below described patents there is either coordination or sequential application of two or more of the above types of reactions to produce desirable components for reformulated gasolines.
For example, a low severity continuous reforming process for naphthas that operates at conditions resulting in low coke formation and producing an improved reformulated gasoline is disclosed in U.S. Pat. No. 5,382,350 to Schmidt. The conditions for this reforming process include high space velocity, relatively high temperature, and low hydrogen to hydrocarbon ratios. The lower severity operation and a high hydrogen yield in this reforming process facilitate the removal of benzene from the reformulated gasoline pool, while diminishing the anticipated hydrogen deficit that reforming could cause. In U.S. Pat. No. 5,196,626 to Child et al., an isoparaffin/olefin alkylation process and reaction system is disclosed in which the liquid acid catalyst inventory is reduced and temperature control is improved by reacting the isoparaffin/olefin feed mixture with a thin film of liquid acid catalyst supported on a heat exchange surface.
A process for the depolymerization and liquefaction of coal to produce a hydrocarbon oil is disclosed in U.S. Pat. No. 4,728,418 to Shabtai et al. The process utilizes a metal chloride catalyst which is intercalated in finely crushed coal and the coal is partially depolymerized under mild hydrotreating conditions during a first processing step. The product from the first step is then subjected to base-catalyzed depolymerization with an alcoholic solution of an alkali hydroxide in a second processing step, and the resulting, fully depolymerized coal is finally hydroprocessed with a sulfided cobalt molybdenum catalyst in a third processing step to obtain a light hydrocarbon oil as the final product.
The above patents relate to processes for production of reformulated hydrocarbon gasoline compositions or light hydrocarbon oils using petroleum-derived streams or fractions or coal as feeds which are nonrenewable sources of energy. Renewable sources such as biomass or its components have been extensively examined as an alternative source for fuels, and in particular oxygenated fuels, e.g., ethanol and various ethers.
For example, U.S. Pat. No. 5,504,259 to Diebold et al. discloses a high temperature (450-550.degree. C.) process for conversion of biomass and refuse derived fuel as feeds into ethers, alcohols, or a mixture thereof. The process comprises pyrolysis of the dried feed in a vortex reactor, catalytically cracking the vapors resulting from the pyrolysis, condensing any aromatic byproduct fraction followed by alkylation of any undesirable benzene present in the fraction, catalytically oligomerizing any ethylene and propylene into higher olefins, isomerizing the olefins to branched olefins, and catalytically reacting the branched olefins with an alcohol to form an alkyl t-alkyl ether suitable as a blending component for reformulated gasoline. Alternatively, the branched olefins can be hydrated with water to produce branched alcohols. Although the final alkyl t-alkyl etheric products of the above process are of value as blending components for reformulated gasoline, the anticipated low selectivity of the initial high-temperature pyrolysis stage of the process and the complexity of the subsequent series of treatments of intermediate products may limit the overall usefulness of the process.
A series of treatments of plant biomass resulting in the production of ethanol, lignin, and other products is disclosed in U.S. Pat. No. 5,735,916 to Lucas et al. Sugars are fermented to ethanol using an existing closed-loop fermentation system which employs genetically engineered thermophilic bacteria. The two desirable products of this process, i.e., lignin and ethanol, are mixed to produce a high energy fuel. In U.S. Pat. No. 5,478,366 to Teo et al., the preparation of a pumpable slurry is disclosed for recovering fuel value from lignin by mixing lignin with water, fuel oil and a dispersing agent, the slurry being defined as a pourable, thixotropic or near Newtonian slurry containing 35-60 wt-% of lignin and suitable for use as a liquid fuel.
A process for chemically converting polyhydric alcohols into a mixture of hydrocarbons and halogen-substituted hydrocarbons is disclosed in U.S. Pat. No. 5,516,960 to Robinson. Also disclosed is a process for conversion of cellulose or hemicellulose to hydrocarbon products of possible value as fuels.
Although the above described patents indicate that biomass or its components can be converted into fuel products, there is no disclosure as to selective conversion of lignin into gasoline, and in particular reformulated partially oxygenated gasoline. Accordingly, a selective process for high-yield conversion of biomass or important biomass components such as lignin into reformulated gasoline and reformulated gasoline blending components is highly desirable.